As the ozone rating in San Antonio continues its slow upward march, area officials are beginning to investigate whether oil and gas drilling in the Eagle Ford Shale has anything to do with it. But their efforts are fraught with complications. And they remain far from answers in what is sure to be a high-stakes debate over the environmental impact of one of the country’s newest and fastest-growing oil and gas development regions.

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That “big stick” is held by the Environmental Protection Agency. For years, San Antonio has touted itself as the largest American city that is in compliance with federal ozone standards, and therefore not subject to extra regulation and enforcement from the EPA. That will soon change. Today, San Antonio is violating the Clean Air Act based on its ozone scores, the highest of which are far above the maximum acceptable value of 75 parts per billion.

“The San Antonio region has really become much more of an interest for ozone problems than it ever was before,” said Daniel Cohan, an associate professor of environmental engineering at Rice University who studies the formation and control of air pollution. Not only have the region’s ozone levels started to increase, but the EPA also lowered its ozone standards from 85 parts per billion to 75 parts per billion in 2008, during the final year of George W. Bush’s presidency.

San Antonio’s ozone uptick is relatively recent. The city’s ozone numbers dropped dramatically in the beginning of the last decade; in 2007, it was under the federal limit even during some of the hottest days of the summer. Starting in the late 2000s, ozone levels began to increase again — just as the first wells were being drilled in the Eagle Ford Shale, now a 400-mile swath of oil and gas production stretching from South Texas’ Mexico border all the way to East Texas, brushing the southern tip of the San Antonio metropolitan area.

That timing has not been lost on anyone. “I think that there can be and there might be impacts” of the oil and gas development, Bella said. This month, AACOG produced its first estimates of the Eagle Ford Shale’s emissions of volatile organic compounds (VOCs) and nitrogen oxides (NOX), air pollutants that are the precursor components of ozone.

The numbers are very preliminary and have not been shared publicly. But they suggest that the oil and gas extraction-related activities in the Eagle Ford Shale result in dozens of tons of emissions of VOCs and NOX every day, according to AACOG’s estimates. Such emissions would be equivalent to as much as half of what’s emitted daily by the entire San Antonio-New Braunfels metropolitan region each day. During a recent health forum in San Antonio, AACOG officials suggested that Eagle Ford activities could increase the city’s ozone score by several parts per billion within the next decade.

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Spokesmen for the Texas Oil and Gas Association and the South Texas Energy & Economic Roundtable, which was established by the 11 largest operators in the Eagle Ford Shale, did not respond to requests for comment.

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Air pollution experts at the Texas Commission on Environmental Quality, which will soon review AACOG’s report and help with revisions, have their own thoughts on the matter. They don’t believe that the Eagle Ford Shale is a major cause of the ozone changes in San Antonio, based on the data they are monitoring.

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This article is available online at texastribune.org/2013/08/01/is-the-eagle-ford-shale-polluting-san-antonio/